U.S. patent application number 11/357023 was filed with the patent office on 2006-08-17 for sheet feeding apparatus and image forming apparatus having the same.
This patent application is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Seiichiro Adachi, Hiroto Koga, Takeshi Suga.
Application Number | 20060180984 11/357023 |
Document ID | / |
Family ID | 34372412 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060180984 |
Kind Code |
A1 |
Suga; Takeshi ; et
al. |
August 17, 2006 |
Sheet feeding apparatus and image forming apparatus having the
same
Abstract
A sheet feeding apparatus for feeding sheets supported by sheet
stacking means capable of ascending and descending by sheet feeding
means is provided. The sheet feeding apparatus includes sheet
position detection means for detecting that an upper surface of a
sheet stack supported by said sheet stacking means reaches a
position whereat it can be fed by said sheet feeding means, blowing
means for blowing air on an end portion of sheets stacked on said
sheet stacking means, and control means for controlling said
blowing means, wherein at least, either when it has been detected
by said sheet position detection means that the sheets reach a
position whereat they can be fed, or before a sheet feeding
operation by said sheet feeding means is started, said control
means performs a blowing operation by said blowing means during
predetermined time.
Inventors: |
Suga; Takeshi; (Ibaraki,
JP) ; Adachi; Seiichiro; (Chiba, JP) ; Koga;
Hiroto; (Chiba, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
Canon Kabushiki Kaisha
Tokyo
JP
|
Family ID: |
34372412 |
Appl. No.: |
11/357023 |
Filed: |
February 21, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10916438 |
Aug 12, 2004 |
|
|
|
11357023 |
Feb 21, 2006 |
|
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Current U.S.
Class: |
271/97 |
Current CPC
Class: |
B65H 2513/53 20130101;
B65H 2513/51 20130101; B65H 2220/09 20130101; B65H 2407/311
20130101; B65H 2513/51 20130101; B65H 2513/53 20130101; B65H
2511/20 20130101; B65H 2511/20 20130101; B65H 3/48 20130101; B65H
2220/01 20130101; B65H 2220/02 20130101; B65H 2220/02 20130101;
B65H 2406/121 20130101 |
Class at
Publication: |
271/097 |
International
Class: |
B65H 3/14 20060101
B65H003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 26, 2003 |
JP |
2003-301029 |
Claims
1-15. (canceled)
16. A sheet feeding apparatus for feeding sheets, comprising: sheet
stacking means for supporting sheets; sheet feeding means for
feeding sheets stacked on said sheet stacking means; blowing means
for blowing air on an end portion of a sheet sheaf stacked on said
sheet stacking means; temperature and humidity detection means for
detecting temperature and humidity in the neighborhood of said
sheet stacking means; control means for controlling said blowing
means to perform a blowing operation before a sheet feeding
operation of said sheet feeding means is started; and a control
table of blowing time in which data of blowing time period of the
blowing means corresponding to the temperature and humidity has
been stored; wherein said control means calls out data of the
blowing time period from said control table of blowing time on the
basis of temperature and humidity information from said temperature
and humidity detection means and controls said blowing means to
perform the blowing operation before the sheet feeding operation
during the blowing time period called from the control table.
17. The sheet feeding apparatus according to claim 16, provided
with said sheet stacking means so as to be able to ascend and
descend, further comprising sheet position detection means for
detecting that an upper surface of a sheet sheaf supported by said
sheet stacking means reaches a position whereat it can be fed by
said sheet feeding means, wherein when it has been detected by said
sheet position detection means that the sheet sheaf reaches a
position whereat it can be fed, said control means calls out a
initial blowing time period from said control table of blowing time
and controls said blowing means to perform the blowing operation
before the sheet feeding operation during the initial blowing time
period.
18. The sheet feeding apparatus according to claim 16, further
comprising: job starting signal generating means for generating a
job starting signal for starting a job, wherein when a job starting
signal has been generated by said job starting signal generating
means, said control means calls out a pre-job blowing time period
from said control table of blowing time and controls said blowing
means to perform the blowing operation before the sheet feeding
operation during the pre-job blowing time period.
19. The sheet feeding apparatus according to claim 17, further
comprising: heating means for heating air to be blown from said
blowing means; and a control table of heating temperature in which
data of temperature of said air to be blown from said blowing means
corresponding to temperature and humidity has been stored, wherein
said control means calls out data of heating temperature from said
control table of heating temperature on the basis of temperature
and humidity information from said temperature and humidity
detection means and controls a heating operation of said heating
means on the basis of the data of heating temperature called from
the control table of heating temperature.
20. The sheet feeding apparatus according to claim 18, further
comprising: heating means for heating air to be blown from said
blowing means; and a control table of heating temperature in which
data of temperature of said air to be blown from said blowing means
corresponding to temperature and humidity has been stored, wherein
said control means calls out data of heating temperature from said
control table of heating temperature on the basis of temperature
and humidity information from said temperature and humidity
detection means and controls a heating operation of said heating
means on the basis of the data of heating temperature from the
control table of heating temperature.
21. A sheet feeding apparatus for feeding sheets, comprising: a
lifter base on which a sheet sheaf has been stacked; a pickup
roller which feeds out sheets from said lifter base; a blow-off
port arranged to oppose to an end portion of the sheet sheaf on
said lifter base; a fan which blows air on an end portion of the
sheet sheaf stacked on said lifter base through said blow-off port;
a temperature and humidity sensor which detects temperature and
humidity in the neighborhood of said lifter base; a controller for
controlling said fan to perform a blowing operation before a sheet
feeding operation of said pickup roller is started; and a control
table of blowing time in which data of blowing time period of the
fan corresponding to the temperature and humidity has been stored;
wherein said controller calls out data of the blowing time period
from said control table of blowing time on the basis of temperature
and humidity information from said temperature and humidity sensor
and controls said fan to perform the blowing operation before the
sheet feeding operation during the blowing time period called from
the control table.
22. The sheet feeding apparatus according to claim 21, provided
with said lifter base so as to be able to ascend and descend,
further comprising: a sheet position detection sensor which detects
an upper surface of the sheet sheaf reaches a position whereat it
can be fed; when it has been detected by said sheet position
detection sensor that the sheet sheaf reaches the position whereat
it can be fed, said controller calls out a initial blowing time
period from said control table of blowing time and controls said
fan to perform the blowing operation before the sheet feeding
operation during the initial blowing time period.
23. The sheet feeding apparatus according to claim 21, further
comprising: job starting signal generating means for generating a
job starting signal for starting a job, wherein when a job starting
signal has been generated by said job starting signal generating
means, said controller calls out a pre-job blowing time period from
said control table of blowing time and controls said fan to be
performed the blowing operation before the sheet feeding operation
during pre-job blowing time period.
24. The sheet feeding apparatus according to claim 22, further
comprising: heater which heats air to be blown from said fan; and a
control table of heating temperature in which data of temperature
of said air to be blown from said fan corresponding to temperature
and humidity has been stored, wherein said control means calls out
data of heating temperature from said control table of heating
temperature on the basis of temperature and humidity information
from said temperature and humidity sensor and controls a heating
operation of said heater on the basis of the data of heating
temperature called from control table of heating temperature.
25. The sheet feeding apparatus according to claim 23, further
comprising: heater which heats air to be blown from said fan; and a
control table of heating temperature in which data of temperature
of said air to be blown from said fan corresponding to temperature
and humidity has been stored, wherein said control means calls out
data of heating temperature from said control table of heating
temperature on the basis of temperature and humidity information
from said temperature and humidity sensor and controls a heating
operation of said heater on the basis of the data of heating
temperature called from control table of heating temperature.
26. An image forming apparatus comprising: an image forming portion
for forming an image on a sheet; and a sheet feeding apparatus for
feeding the sheet to said image forming portion according to any
one of said claims 16 to 25.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a sheet feeding apparatus
and an image forming apparatus having the same, and more
particularly to structure for separating and feeding sheets having
high adhesion properties between those sheets.
[0003] 2. Related Background Art
[0004] A conventional image forming apparatus such as a copying
machine and a printer has had a sheet feeding apparatus which after
feeding out sheets stacked on sheet stacking means one sheet at a
time from one at the uppermost position in order by a pickup roller
which is sheet feeding means, separates one sheet at a time by a
separating portion for feeding to an image forming portion.
[0005] In this case, when continuous sheets feeding is performed in
such a sheet feeding apparatus, cut sheets are used, and such cut
sheets have been normally limited to woodfree paper or standard
sheets designated by the copying machine manufacturer. Also, in
order to reliably separate such sheets one sheet at a time for
feeding, various separating methods have been conventionally
adopted, and as such a separating system, there is, for example, a
separating pad system in which a frictional member is caused to
abut against a feed roller at predetermined pressure for preventing
double feeding.
[0006] Also, as another separating system, there is a retard
separating system in which a feed roller for rotating in a sheet
conveying direction and a separating roller which is driven in a
direction opposite to the sheet conveying direction at
predetermined torque and abuts against the feed roller at
predetermined pressure constitute a separating portion, and by this
separating portion, only the sheet at the uppermost level of a
sheet stack sent out by the pickup roller is caused to pass
through, and another sheet which has been accompanied by the
uppermost sheet and fed is returned on the sheet stacking means
side to thereby prevent double feeding.
[0007] In this case, in order to reliably separate and feed sheets
by these separating systems, in the case of, for example, the
retard separating system, it has become possible to reliably
separate sheets one sheet at a time by optimizing the return torque
of the separating roller and the applied pressure by taking into
consideration the frictional force of the sheet to be fed.
[0008] In recent years, along with the diversification of sheets
(recording media), there has been growing a request for forming an
image also on a sheet such as a coated sheet obtained by performing
coating processing on the surface of a sheet in order to give
brightness or a gloss from the request from the market for
colorization in addition to ultra-thick paper, an OHP sheet, art
film and the like.
[0009] When the ultra-thick paper is going to be fed, however, the
dead load of the ultra-thick paper becomes conveying resistance and
the paper cannot be picked up, but paper jam occurs. Also, sheets
made of resin material easy to be charged with electricity as in
the case of the OHP sheet or the art film are incapable of picking
up or cause double feeding because during a feeding operation under
a low humidity environment, sheets rub against each other, whereby
their sheet surfaces are gradually charged with electricity and the
sheets come to stick to each other by Coulomb forces.
[0010] Also, in coated sheets obtained by coating the surface of a
sheet with coating material consisting of paint or the like, since
the coated sheets have a property that the sheets attract each
other particularly when stacking under a high humidity environment,
there arises a problem that pickup cannot be performed and double
feeding occurs frequently.
[0011] This is because although in the case of such a specialty
sheet as described above, a frictional force itself between the
sheets themselves is equal to or less than that of standard sheet
and the like, in the case of resin material sheets, by means of an
attraction force due to frictional charging under the low humidity
environment, and in the case of the coated sheet, by means of an
attraction force under the high humidity environment, the
attraction is performed by a far higher force than the frictional
force between the sheets themselves, and therefore, separation can
be hardly made by the conventional separating system.
[0012] In other words, in the conventional separating system, since
only the frictional force between the sheets themselves has been
taken into consideration, the sheets cannot be reliably separated
when such an attraction force other than the frictional force is
exerted.
[0013] Thus, in order to nullify such a very high attraction force
between the sheets themselves, there is a separation feeding system
in which as disclosed in Japanese Patent Application Laid-Open No.
H11-005643, air is blown from the side of the sheet stack to ravel
the sheets in advance; in a state in which any attraction between
the sheets has been nullified, the sheets are picked up one sheet
at a time from a sheet at a higher position; and the sheets are
separated one sheet at a time at a separating portion provided at
the downstream portion. Apparatuses in which this separation
feeding system has been adopted have been used in the printing
business world or in some copying machines.
[0014] In the separation feeding system having means (hereinafter,
referred to as auxiliary air raveling means) for blowing air from
the side of such a sheet stack, since even sheets (recording media)
having such a high attraction force as described above nullify the
attraction by raveling the sheets prior to feeding, the separation
performance has been improved as compared with the system utilizing
only the frictional force described above.
[0015] FIG. 15 is a view showing structure of a sheet feeding
apparatus having such auxiliary air raveling means, and this sheet
feeding apparatus 155 has: a sheets feeding tray 59 for stacking
sheets S; sheet feeding means (not shown) for sending out a sheet S
from the sheets feeding tray 59; air blowing means 71 for blowing
air on the side of the sheets S stacked; and flow path moving means
157 for moving the air blowing means 71 in the vertical direction
along the side of the sheet S in a vertical direction.
[0016] The flow path moving means 157 has: a guide rail (not shown)
for supporting the air blowing means 71 in a perpendicular
direction in such a manner as to be freely movable; an electrical
motor 121; and a cam plate 123 fixed to the output shaft of this
electrical motor 121, for moving the air blowing means 71 by
slidably contacting the underside of the air blowing means 71.
[0017] In such a flow path moving means 157, when the electrical
motor 121 rotates, the cam plate 123 causes the air blowing means
71 to move in the vertical direction, and accordingly, an air
course is to move in the vertical direction. In this case, since an
opening (air duct port) of the air blowing means 71 has an opening
area which is constant always, when the air blowing means 71
lowers, the side of the sheet S is to face the opening, whereby the
area of the opening is reduced, and air to be blown off from the
opening is to be narrowed down. As a result, it becomes possible to
nullify the attraction between all the sheets by causing the sheet
S at a higher position to float in the air.
[0018] In this respect, as the separation feeding system in which
air has been arranged to be flown from the side of the sheet stack
as described above, there is a sheet feeding apparatus in which as
disclosed in Japanese Patent Laid-Open No. 2001-48366, the blown
air is heated by a heater to thereby dehumidify the sheets and the
attraction force of the sheets (coated sheets) particularly under a
high humidity environment has been mitigated.
[0019] In the sheet feeding apparatus in which the separation
feeding system for blowing air from the side of the sheet stack has
been adopted, however, when air is blown, only the neighborhood of
the air blowoff port of the sheets stacked is partially dried
particularly under a low humidity environment.
[0020] Thus, when the sheets are partially dried as described
above, unevenness develops in the surface resistance value within
the sheet surface, and as a result, when the sheet is fed to an
image forming portion of the image forming apparatus, this dried
portion causes a transfer failure, resulting in an image defect.
Particularly, in the case of an electrophotography system in which
the image forming portion transfers a toner image on the sheet
through the use of static electricity, since the transfer
performance greatly depends upon the surface resistance value of
the sheet surface, when unevenness develops in the surface
resistance value, transfer unevenness occurs, image deterioration
due to it is conspicuous, and becomes very unsightly.
SUMMARY OF THE INVENTION
[0021] The present invention has been achieved in view of the
above-mentioned state of affairs, and is aimed to provide a sheet
feeding apparatus capable of reliably separating and feeding sheets
without causing image defects such as transfer failures, and an
image forming apparatus having the same.
[0022] According to one aspect of the present invention, a sheet
feeding apparatus for feeding sheets supported by liftable sheet
stacking means, comprising:
[0023] sheet feeding means for feeding a sheet supported on said
sheet stacking means;
[0024] sheet position detection means for detecting that an upper
surface of a sheet stack supported by said sheet stacking means
reaches a feeding position whereat it can be fed by said sheet
feeding means;
[0025] blowing means for blowing air on an end portion of sheets
stacked on said sheet stacking means; and
[0026] control means for controlling said blowing means,
wherein
[0027] at least, either when it has been detected by said sheet
position detection means that the upper surface of the sheet stack
reach the feeding position, or before a sheet feeding operation by
said sheet feeding means is started, said control means performs a
blowing operation by said blowing means during a predetermined
time.
[0028] According to another aspect of the invention, a sheet
feeding apparatus for feeding sheets, comprising:
[0029] a lifter base on which a sheet stack has been stacked; a
pickup roller for sending out sheets from said lifter base;
[0030] an air duct port arranged to oppose to an end portion of the
sheet stack on said lifter base;
[0031] a fan for blowing air through said air duct port;
[0032] a sheet surface position detection sensor for detecting, by
raising said lifter base, that an upper surface of the sheet stack
reaches a feeding position whereat it can be fed; and
[0033] a controller for controlling an operation of said fan,
wherein
[0034] at least either when it has been detected by said sheet
surface position detection sensor that the sheet stack reaches the
feeding position whereat, or before a sheet feeding operation by
said pickup roller is started, said fan is caused to perform a
blowing operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a cross-sectional view showing a printer, which is
an example of an image forming apparatus having a sheet feeding
apparatus according to an example of the present invention;
[0036] FIG. 2 is a plan view showing structure of the
above-described sheet feeding apparatus;
[0037] FIG. 3 is a side cross-sectional view showing the
above-described sheet feeding apparatus;
[0038] FIG. 4 is a block diagram showing the above-described
printer;
[0039] FIG. 5 is a graphic chart showing relationship between an
attraction force and relative humidity;
[0040] FIGS. 6A, 6B, 6C and 6D are views explaining an attraction
mechanism of coated sheet;
[0041] FIG. 7 is a plan view showing a state when the
above-described sheet feeding apparatus has housed small-sized
sheets;
[0042] FIG. 8 is a graphic chart showing temporal change of
attraction force since immediately after opened;
[0043] FIG. 9 is a graphic chart showing temporal change of
attraction force after raveling;
[0044] FIG. 10 is a control table for controlling initial swing
time of the above-described sheet feeding apparatus;
[0045] FIG. 11 is a control table for controlling pre-job swing
time of the above-described sheet feeding apparatus;
[0046] FIG. 12 is a control table for controlling temperature for
heater temperature control of the above-described sheet feeding
apparatus;
[0047] FIG. 13 is a flow chart showing an initial swing operation
of the above-described sheet feeding apparatus;
[0048] FIG. 14 is a flow chart showing a pre-job swing operation of
the above-described sheet feeding apparatus; and
[0049] FIG. 15 is a view for explaining conventional structure of
the sheet feeding apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] Hereinafter, with reference to the drawings, the detailed
description will be made of the best example for carrying out the
present invention.
[0051] FIG. 1 is a cross-sectional view showing a printer, which is
an example of an image forming apparatus having a sheet feeding
apparatus according to an example of the present invention.
[0052] In FIG. 1, reference numeral 1000 denotes a printer, and
this printer 1000 has a main body 1001 of the printer, and a
scanner 2000 arranged on the upper surface of the main body 1001 of
the printer.
[0053] Here, the scanner 2000 for reading an original includes: a
scanning optical system light source 201; platen glass 202; an
original pressure plate 203 for opening and closing; a lens 204; a
light receiving element (photoelectric conversion) 205; an image
processing portion 206; a memory portion 208 for storing an image
processing signal processed at the image processing portion 206,
and the like.
[0054] Thus, when reading the original, the original is read by
irradiating light on the original (not shown) placed on the platen
glass 202 by the scanning optical system light source 201. Thus,
after the original image thus read is processed by the image
processing portion 206, it is converted into an
electrically-encoded electric signal 207 to be transmitted to a
laser scanner 111a, which is image forming means. In this respect,
it is also possible to cause the image information which has been
processed by the image processing portion 206 and been encoded to
be stored in the memory portion 208 once, and to transmit it to the
laser scanner 111a as the need arises by means of a signal from a
controller 120 to be described later.
[0055] The main body 1001 of the printer includes: a sheet feeding
apparatus 1002 for feeding a sheet S; a sheet conveying apparatus
1004 for conveying a sheet S fed by the sheet feeding apparatus
1002 to an image forming portion 1003; a controller 120, which is
control means for controlling the printer 1000, and the like.
[0056] In this case, the sheet feeding apparatus 1002 includes: a
cassette 100; the pickup roller 101; and a separation portion
consisting of a feed roller 102 and a retard roller 103, and the
sheets S within the cassette 100 are adapted to be separated and
fed one sheet at a time by an operation of the pickup roller 101
which ascends and descends/rotates at predetermined timing and the
separation portion. Also, in the neighborhood of the feed roller
102 and the retard roller 103 on the downstream side in the sheet
conveying direction, there is provided a sheet feeding sensor 104,
and the structure is arranged such that passage of the sheet S can
be detected by this sheet feeding sensor 104.
[0057] Also, in the lower part of the main body 1001 of the
printer, there is provided a cassette storage 1005 in which a
cassette 100 is stored, and this cassette storage 1005 is
partitioned by partition plates 106, 107, and is hermetically
sealed with a predetermined degree of sealing. In this respect, in
the cassette 100, there are arranged temperature and relative
humidity sensors 108 respectively, which are temperature and
humidity detection means for detecting the temperature and humidity
in the neighborhood of the cassette within the storage, and the
temperature and humidity in each cassette storage 1005 are adapted
to be able to be detected independently respectively.
[0058] In this respect, reference numeral 1010 denotes a detachably
mountable paper deck having large capacity, available as an option,
and this paper deck 1010 is provided with a sheet feeding apparatus
1002 having the same structure as the main body 1001 of the printer
and a lifter base (not shown) capable of ascending and descending.
Also, this paper deck 1010 is hermetically sealed with a
predetermined degree of sealing, and is provided with the
temperature and humidity sensors 108 for detecting temperature and
humidity within the deck portion.
[0059] The sheet conveying apparatus 1004 includes a conveying
roller pair 105 and a registration roller portion having a
registration pre-roller pair 130 and a registration roller pair
110, and the sheet S fed from the sheet feeding apparatus 1002 is
adapted to be guided to the registration roller pair 110 by the
conveying roller pair 105 after passing through a sheet conveying
path 108 to be constituted by a guide plate. Further, the sheet S
is thereafter adapted to be conveyed to the image forming portion
1003 by the registration roller pair 110.
[0060] The image forming portion 1003 includes: a photosensitive
drum 112; the laser scanner 111a; a developing device 114; a
transfer charger 115; a separation charger 116 and the like, and on
forming an image, laser light from the laser scanner 111a is folded
back by a mirror 113, and is irradiated on an exposure position
112a on the photosensitive drum which is rotating in the clockwise
direction, whereby a latent image is formed on the photosensitive
drum, and the latent image further formed on the photosensitive
drum by performing as described above is adapted to be visualized
as a toner image thereafter by the developing device 114.
[0061] In this respect, the toner image on this photosensitive drum
is thereafter transferred on the sheet S by the transfer charger
115 in a transfer portion 112b. Further, the sheet S on which the
toner image has been transferred as described above is, after
electrostatically separated from the photosensitive drum 112 by the
separation charger 116, conveyed to a fixing apparatus 118 by means
of a conveying belt 117 for fixing the toner image, and thereafter,
is discharged by a discharge roller 119. Also, in a conveying route
between the fixing apparatus 118 and the discharge roller 119,
there is provided a sheet discharge sensor 119a, and the structure
is arranged such that passage of the sheet S to be discharged can
be detected by this sheet discharge sensor 119a.
[0062] In this respect, in the present example, although the main
body 1001 of the printer is separate from the scanner 2000, the
main body 1001 of the printer may be also integral with the scanner
2000. Also, whether the main body 1001 of the printer is separate
from or integral with the scanner 2000, if a processing signal of
the scanner 2000 is inputted into the laser scanner 111a, it will
function as a copying machine, and if a transmission signal of FAX
is inputted, it will function as a facsimile. Further, if an output
signal of a personal computer is inputted, it will function as a
printer.
[0063] If a processing signal of the image processing portion 206
of the scanner 2000 is transmitted to another FAX conversely, it
will function as FAX. Also, if in the scanner 2000, such an
original automatic feeding apparatus 250 as indicated by a two-dot
chain line is mounted in place of the pressure plate 203, the
original will be also able to be automatically read.
[0064] FIG. 2 is a plan view showing structure of the sheet feeding
apparatus 1002, and FIG. 3 is a side cross-sectional view showing
the sheet feeding apparatus. In this respect, in the present
example, the cassette 100 is attached to or detached from the
cassette storage 1005 in a widthwise direction perpendicular to the
sheet conveying direction.
[0065] In FIG. 2, reference numeral 1, 2 denotes a side regulation
plate, which is a regulation member for regulating a position in a
widthwise direction of sheets S stacked and housed within the
cassette 100, and these side regulation plates 1, 2 are constructed
to be able to move in a widthwise direction in accordance with a
size of the sheets S. Also, reference numeral 3 denotes a rear end
regulation plate for regulating a rear end position of the sheets S
in the sheet conveying direction, and this rear end regulation
plate 3 is constructed to be able to move in the sheet conveying
direction in accordance with the size of the sheets S.
[0066] In this respect, the cassette 100 is adapted to be able to
be drawn out along rails 19, 20 shown in FIG. 3, and when the user
sets the sheets S, the cassette 100 can be drawn out on this side
from the main body 1001 of the printer. Also, the cassette 100 is
provided with a protruded portion 100a as shown in FIG. 2, and when
the cassette 100 is housed within the cassette storage 1005, this
protruded portion 100a is adapted to be detected by a cassette
attachment and detachment detection sensor 17 provided in the
cassette storage 1005.
[0067] Thus, a detection signal from this cassette attachment and
detachment detection sensor 17 is transmitted to a controller 120,
and the controller 120 is adapted to be able to detect, on the
basis of the detection signal from this cassette attachment and
detachment detection sensor 17, whether the cassette 100 has been
mounted in the cassette storage 1005 or has been drawn out.
[0068] Also, within the cassette 100, there is provided a lifter
base 16, which is sheet stacking means capable of ascending and
descending for stacking the sheets S as shown in FIG. 3, and this
lifter base 16 is adapted to ascend or descend depending upon
attachment or detachment of the cassette 100 by a lifter motor 18
shown in FIG. 4.
[0069] For example, when the user houses the cassette 100 in which
the sheets S have been set and detects it on the basis of a signal
from the cassette attachment and detachment detection sensor 17,
the controller 120 is adapted to drive the lifter motor 18 for
raising the lifter base 16. Also, when in order to set the sheets,
the user draws out the cassette 100 to detect it on the basis of a
signal from the cassette attachment and detachment detection sensor
17, the lifter motor 18 is adapted to operate so as to lower the
lifter base 16 to a lower limit position.
[0070] In this respect, in the upper part of the cassette storage
1005, there is provided a sheet surface position detection sensor
15 for detecting whether or not the sheet surface position of a
sheet at the uppermost position stacked on the lifter base 16 is at
an appropriate height for feeding, that is, that it has reached a
position whereat the sheet can be fed.
[0071] Thus, when the lifter base 16 rises, the lifter motor 18
rotates before the sheet surface position detection sensor 15,
which is this sheet position detection means, detects the sheet
surface position of the sheet S1 at the uppermost position. When
the sheet surface position detection sensor 15 detects the sheet S1
at the uppermost position, however, the controller 120 is adapted
to stop the lifter motor 18 on the basis of the detection signal
from this sheet surface position detection sensor 15. Thereby, the
appropriate height of sheet surface can be maintained.
[0072] In this respect, when with the feeding operation, the sheets
S are fed from the higher one in order, the height of sheet surface
gradually lowers and the sheet surface position detection sensor 15
becomes OFF, the controller 120 is adapted to drive the lifter
motor 18 again so as to raise the lifter base 16. Thereby, the
height of sheet surface can be controlled within a constant range
always.
[0073] Although in the case of coated sheets, an attraction
phenomenon occurs under a high humidity environment as described
above, the description will be made of the elucidation of the
attraction mechanism conducted by the present inventor.
[0074] FIG. 5 shows results of an attraction force measurement
experiment made by the present inventor in advance on elucidating
the attraction mechanism. In this attraction force measurement
experiment, attraction forces of two kinds of coated sheets (coated
sheets A and B) and a standard sheet have been measured with the
environment varied. In this respect, in FIG. 5, relative humidity
during the experiment is indicated on the abscissa and the
attraction force, on the ordinate, and the temperature is fixed at
30.degree. C. for measurement.
[0075] As will be apparent from the results shown in FIG. 5, the
attraction force of the coated sheets A and B has very high
temperature dependence much unlike the standard sheets, and in an
environment at relative humidity of 40% or less, the coated sheets
hardly generate any attraction force as in the case of the standard
sheets. However, it can be seen that when the relative humidity
exceeds 40%, the attraction force linearly increases. Also,
although similar measurements have been made at temperatures of
20.degree. C. and 40.degree. C., the same results have been
obtained. From the foregoing, it has turned out that the attraction
force of the coated sheets strongly depends upon the relative
humidity rather than absolute water content in the air.
[0076] The attraction mechanism of the coated sheets could be
elucidated by various experiments by the present inventor as
below.
[0077] When a sheet stack SA of the coated sheets is exposed under
a high humidity environment as shown in FIG. 6A, only the surface
of the uppermost sheet S1 of the sheet stack SA and the side edge
portion of the sheet stack SA absorb moisture. When moisture is
absorbed as described above, the surface of the uppermost sheet S1
elongates and the side edge portion of the sheet stack SA swells as
shown in FIG. 6B.
[0078] In this case, in the uppermost sheet S1, since the back
surface hardly elongates though the surface elongates, a convex
deformation phenomenon occurs on the uppermost sheet S1 as shown in
FIG. 6C. At this time, since the coated sheet has high evenness and
low gas permeability, air hardly flows into between the sheets. For
this reason, when the convex deformation phenomenon occurs on the
uppermost sheet S1, the volume between the uppermost sheet S1 and
the next uppermost sheet S2 expands to cause negative pressure, and
there occurs a phenomenon (hereinafter, referred to as uppermost
sheet moisture absorption attraction) in which the next uppermost
sheet S2 is attracted into the uppermost sheet S1.
[0079] Also, when in any sheet stack SA other than the uppermost
sheet, the side edge portion absorbs moisture, the side edge
portion swells, but a central portion of the sheet stack SA does
not swell even if the side edge portion swells as described above.
Therefore, the volume expands in a width-wise direction of the
sheet, and accordingly there occurs a phenomenon (hereinafter,
referred to as side edge portion moisture absorption attraction) in
which negative pressure develops between the sheets for
attracting.
[0080] Further, when convex deformation also occurs on the second
uppermost coated sheet S2 under the influence of the convex
deformation of the uppermost sheet S1 as shown in FIG. 6D, there
may occur a phenomenon (hereinafter, referred to as chain
deformation attraction) in which negative pressure develops between
the second coated sheet S2 and the third coated sheet S3 for
attracting. In this respect, this chain deformation attraction may
similarly occur over the third sheet and downward several tens of
sheets.
[0081] As described above, as a mechanism of coated sheet
attraction under high humidity, there exist three types of
attraction phenomena: uppermost sheet moisture absorption and
attraction, side edge portion moisture absorption and attraction,
and chain deformation attraction. In this case, since the cause of
these three types of attraction phenomena is that the coated sheet
absorbs moisture to swell, or elongates to cause negative pressure,
if air is caused to flow into between the coated sheets for
nullifying the negative pressure, the attraction phenomenon will be
able to be eliminated. Further, by heating air for flowing in to
high temperature, the coated sheets which have absorbed moisture
can be dehumidified and dried for restricting the swelling, whereby
it is possible to restrict the phenomenon in which the coated
sheets themselves will attract each other again.
[0082] In the present example, so as to flow air into between the
coated sheets as described above, of the side regulation plates
1,2, on the side regulation plate 2 on the back side in a widthwise
direction, a plurality (at two places, in the present example) of
air duct ports 2a, 2b are provided at a predetermined interval in
the sheet conveying direction as shown in FIGS. 2 and 3, and are
formed at a height position for facing the side of the sheets S
located at least at a position whereat they can be fed. These air
duct ports 2a, 2b are provided with ducts 9, 12 in which there are
installed therein fans 4, 5 which are blowing means, and air is
blown on the sheets S through the air duct port 2a, 2b by the fans
4, 5.
[0083] In this respect, between the fan 4,5 and the air duct port
2a, 2b, there is provided a shutter 10, 11 so as to be able to
ascend or descend, and this shutter 10, 11 is adapted to be able to
ascend or descend by a swing motor 13 and an elevator mechanism
(not shown). When blowing air onto the sheets S, this shutter 10,
11 is caused to gradually move up or down for swinging air to be
blown up or down, whereby the air is blown into between the sheets
in order and the sheets raveling effect can be enhanced.
[0084] In this respect, these fans 4, 5 and the swing motor 13 are
adapted to be driven independently respectively on the basis of a
signal from a controller 120 to be inputted via fan driver circuits
4a, 5a and a swing motor driver circuit 13a which are shown in FIG.
4.
[0085] Further, the structure is arranged such that as shown in
FIG. 2, in the neighborhood of an intake port 9a of a duct 9
provided at the air-blow port 2a on the pickup roller side, there
is provided air heating means 8, which is heating means consisting
of a heater 6 and a heat sink 7, and that by means of the air
heating means 8 provided on the upstream side of this fan 5 in the
air blowing-off direction, air inhaled from the intake port 9a in a
direction indicated by an arrow can be heated before blown off, and
be blown off through the air duct port 2a.
[0086] In this respect, to the heat sink 7, there is installed a
thermistor 7a for detecting temperature on the surface of the heat
sink, and a detection-signal from this thermistor 7a is adapted to
be transmitted to the controller 120 as shown in FIG. 4. Thus, the
controller 120 ON/OFF-controls a heater 6 of the air heating means
8 via the driver circuit 6a in response to the detection signal
from this thermistor 7a, whereby temperature of warm air from the
air duct port 2a is adapted to be able to be controlled.
[0087] As shown in FIG. 2, the fans 4, 5, the ducts 9, 12, the air
heating means 8, the shutters 10, 11 and the like are all
integrally installed to the side regulation plate 2 on the back
side in the widthwise direction. Thereby, even if the sheet S is
changed from the size shown in FIG. 2 to the sheet S2 of a smaller
size shown in FIG. 7, the positional relationship with the end
portion of the sheet S2 can be always maintained because the fan 5
and the like also move integrally together with the side regulation
plate 2 on the back side in the widthwise direction
accordingly.
[0088] In this respect, when like the sheet S2 of a smaller size
shown in FIG. 7, the position of the rear end of the sheet S2 does
not reach the air duct port 2b on the downstream in the sheet
conveying direction, blowing by the fan 4 is wasted even if the fan
4 is driven.
[0089] For this reason, when the controller 120 is provided in the
cassette 100 and the sheet S housed within the cassette 100 is
judged to be a sheet of a small size on the basis of a sheet size
information signal from a sheet size detection sensor 14 shown in
FIG. 4 for detecting the sheet size in response to, for example,
positions of the side regulation plate 1, 2 and the rear end
regulation plate 3, driving of the fan 4 is adapted to be stopped
independently.
[0090] Thus, air is caused to flow into between the sheets for
nullifying the negative pressure as described above, and the coated
sheets which have absorbed moisture by heating the air for flowing
in to high temperature are dehumidified and dried, whereby it is
possible to restrict the swelling and to restrict the phenomenon in
which the coated sheets themselves will attract each other.
[0091] On the other hand, the present inventor has discovered by
experiment that as a characteristic of the coated sheet, the
attraction force reaches the uppermost one immediately after the
coated sheet is opened from its wrapping paper.
[0092] FIG. 8 is a view showing data obtained by measuring temporal
change of attraction force of the coated sheet since during
opening. In this respect, in FIG. 8, the attraction force is
indicated on the ordinate, and time, on the abscissa. Also, the
environment during this measurement is 30.degree. C. and 80%.
[0093] As will be apparent from the measurement result shown in
FIG. 8, the attraction force of the coated sheet is at the
uppermost immediately after opened, and lowers gradually with the
lapse of time. In other words, the attraction force of the coated
sheet becomes the uppermost one immediately after the user houses
the coated sheets within the cassette and the cassette 100 is
housed within the cassette storage 1005. Hereinafter, this
attraction phenomenon is referred to as attraction immediately
after opened.
[0094] Next, the present inventor has caused high-temperature air
to flow into between the coated sheets attracted for raveling and
measured temporal change of attraction force after the attraction
force has been nullified. FIG. 9 is a view showing data obtained by
measuring the temporal change of attraction force after the
attraction force has been nullified. In this respect, in FIG. 9,
the attraction force is indicated on the ordinate, and time, on the
abscissa.
[0095] As will be apparent from the measurement result shown in
FIG. 9, although the attraction force has been nullified
immediately after the raveling, re-attraction gradually starts with
the lapse of time, and the attraction force has considerably
developed although the magnitude of the attraction force
immediately after opened is not reached. Hereinafter, this
attraction phenomenon is referred to as re-attraction after left
standing. It has turned out that such a re-attraction after left
standing and the attraction immediately after opened already
described also cause double feeding or mis-feeding.
[0096] Further, in order to investigate an influence upon an image
(transfer property) by partial drying of the coated sheet due to
high-temperature air, the present inventor has measured partial
water content of the coated sheet when warm air at 45.degree. C. is
blown for one minute under an environment of 30.degree. C.80% and
5.degree. C.10%. As a result, unevenness of water content could be
hardly observed under the environment of 30.degree. C.80%, and it
turned out that unevenness of water content markedly occurs under
the environment of 5.degree. C.10%.
[0097] Also, when an image is transferred by the image forming
portion 1003 through the use of these coated sheets, there has been
no problem at all with the coated sheet at the time of 30.degree.
C.80%, but in the image at the time of 5.degree. C.10%, it could be
confirmed that the transfer becomes weaker at places partially less
water content and no density appears.
[0098] In other words, it has turned out that although the coated
sheet markedly attracts under high-temperature high-humidity
environment, the image is not affected even if it is raveled by
high-temperature air, but since attraction of the coated sheet does
not occur under low-humidity low-temperature environment
conversely, it is not necessary to ravel with high-temperature air
blown, but when blown, an image defect occurs conversely.
[0099] Also, it has turned out that an image defect due to transfer
failure under low-humidity environment is in correlation with
blowing time period and blowing speed of air in addition to
temperature of the air.
[0100] Thus, on the basis of these elucidation results, in the
present embodiment, the structure has been arranged as below.
[0101] That is, since attraction occurs with the coated sheet
immediately after opened, when the sheet surface of the coated
sheet is detected by the sheet surface position detection sensor 15
after the cassette 100 is mounted in the cassette storage 1005,
that is, when the coated sheet reaches a position whereat it can be
fed, blowing is first performed for a predetermined time period T1
for raveling sufficiently. This operation is hereinafter referred
to as initial swing operation.
[0102] Also, in order to nullify the re-attraction after left
standing, blowing has been performed for a predetermined time
period T2 prior to starting the feeding operation, and the raveling
operation has also been performed sufficiently. This operation is
hereinafter referred to as pre-job swing operation. Further, in the
case of the coated sheet, since it attracts very strongly under
high-humidity environment and no attraction occurs under
low-humidity environment as described already, the temperature for
temperature control of the heater 6 has been set in response to
each environment.
[0103] At least one of the initial swing operation and the pre-job
swing operation is performed prior to starting the feeding
operation as described above, whereby it is possible to bring the
coated sheets in a reliably raveled state during sheets feeding. In
this respect, in the present invention, "prior to starting the
feeding operation" includes both when sheets for performing the
initial swing operation reach a position whereat they can be fed,
and when in order to perform the pre-job swing operation, a job
starting button as job starting signal generating means for
generating a job starting signal for starting the job has been
depressed by an user to be described later.
[0104] FIGS. 10 to 12 are control tables concerning optimum air
blowing time (initial swing time T1, pre-job swing time T2) and
temperature of air (temperature for temperature control of heater
6) formed by the present inventor by taking into consideration an
influence upon transfer property under each environment in which
the sheet feeding apparatus 1002 is used. In this respect, a
control table of blowing time, a control table of heating
temperature, a control table of heating temperature and a control
table of fan blowing speed in the initial swing and the pre-job
swing shown in these FIGS. 10 to 12 have been stored in the storing
means 30 shown in FIG. 4.
[0105] Thus, when sheets to be set in the cassette 100 have been
set to be, for example, coated sheets in the sheet kind input
portion 21 in the operation portion shown in FIG. 4, at a point of
time whereat the cassette 100 has been mounted in the cassette
storage 1005, the initial swing has been to be performed by a
predetermined time T1 in response to environmental conditions
within the cassette storage 1005 or the cassette 100.
[0106] In this respect, since neither attraction immediately after
opened under a high-humidity environment nor re-attraction after
left standing occurs with sheets made of resin material such as OHP
and art film, the initial swing or the pre-job swing may not be
performed. Also, since the attraction mechanism is also application
by charging, it is not necessary to heat air by the heater 6.
Thereby, time for the heater 6 to complete the temperature control
can be reduced.
[0107] Also, in the case of standard sheets, since they naturally
do not attract, the raveling operation due to air during the
feeding operation is not required. When not required as described
above, the initial swing, the pre-job swing and temperature control
of the heater 6 will not be performed as much as possible, whereby
the user can use the printer comfortably because FCOT becomes
faster.
[0108] Next, with reference to the flow chart shown in FIG. 13, the
description will be made of the initial swing operation.
[0109] When the cassette 100 is mounted in the cassette storage
1005 and the cassette attachment and detachment detection sensor 17
which has detected it is turned ON (Y of Step 1), the controller
120 rotationally drives the lifter motor 18 in a direction to raise
the lifter base 16 (Step 2). Thereafter, the position of the sheet
surface gradually rises together with the lifter base 16, and when
soon the sheet surface position detection sensor 15 detects the
sheet surface to turn ON (Y of Step 3), the lifter motor 18 is
caused to stop (Step 4).
[0110] Next, the temperature and humidity sensor 108 detects
temperature and humidity within the cassette storage (cassette 100)
(Step 5), and the controller 120 calls out data on temperature for
heater 6 temperature control and the initial swing time T1 from the
control tables shown in FIGS. 10 and 12 on the basis of these
temperature and humidity detected (Step 6). Thus, the heater 6 is
electrically energized via the heater driver circuit 6a (See FIG.
4) to perform temperature control of the heater 6.
[0111] Next, when temperature control of the heater 6 is completed
(Y of Step 7), the fans 4, 5 and the swing motor 6 are turned ON
(Step 8). Thereafter, when the initial swing time T1 obtained from
the control table elapses (Y of Step 9), the fans 4, 5 and the
swing motor 6 are turned OFF (stopped) (Step 10).
[0112] Thus, immediately after opened as described above, air
heated is blown on the coated sheets, whereby it is possible to
nullify the attraction between the coated sheets and to reliably
ravel the coated sheets. Thereby, it is possible to provide a
highly reliable sheet feeding apparatus in which jamming and double
feeding do not occur. Also, as regards this initial swing time T1
and the temperature for temperature control, since an optimum table
obtained by experiments so as to make the raveling ability of
coated sheets and the image quality compatible is used, image
deterioration such as transfer failure does not occur as a matter
of course.
[0113] In this respect, when there is a possibility that the coated
sheets have not been sufficiently raveled in the initial swing
operation, any job starting may not be accepted before the initial
swing operation is completed, or after the job starting is accepted
once, the job may be started after the completion of the initial
swing operation.
[0114] Next, with reference to the flow chart shown in FIG. 14, the
description will be made of the pre-job swing operation to be
performed prior to starting the feeding operation in order to
nullify the re-attraction after left standing.
[0115] When a job starting button as job starting signal generating
means for generating a job starting signal for starting the job is
depressed by the user, the temperature and humidity sensor 108
first detects temperature and humidity within the cassette storage
(cassette 100) (Step 21), and the controller 120 calls out data of
the pre-job swing time T2 and the temperature for temperature
control of the heater 6 temperature control from the control table
shown in FIGS. 11 and 12 on the basis of these temperature and
humidity detected (Step 22).
[0116] Thus, the heater 6 is electrically energized on the basis of
the data of the temperature for temperature control called out to
perform temperature control of the heater 6, and when the
temperature control of the heater 6 is completed (Y of Step 23),
the fans 4, 5 and the swing motor 6 are turned ON (Step 24).
Thereafter, when the pre-job swing time T2 obtained from the
control table elapses (Y of Step 25), the feeding operation is
started (Step 26). When the predetermined job is completed, that
is, when the last sheet of the job is fed (Y of Step 27), the fans
4, 5 and the swing motor 6 are turned OFF (stopped) (Step 28).
[0117] Thus, before starting the feeding operation after left
standing as described above, air heated is blown on the coated
sheets, whereby it is possible to nullify the re-attraction for
reliably raveling the coated sheets.
[0118] When the sheets reach a position whereat they can be fed and
before the sheet feeding operation is started, the air is blown
from the side of the sheets S during predetermined time T1, T2,
whereby it is possible to reliably separate and feed the various
sheets such as coated sheets, OHP, art film and ultra thick paper
without causing image defects such as transfer failure.
[0119] Also, the temperature for temperature control of the heater
6 is set on the basis of a signal from the temperature and humidity
sensor 108 provided in the neighborhood of the cassette 100,
whereby it is possible to provide a good-quality image free from
image defects such as transfer failure together with achieving good
feeding performance.
[0120] In this respect, in the foregoing description, the
description has been made of a case where air is blown from the
side of the sheets by performing both the initial swing and the
pre-job swing when mounting a cassette and before the feeding
operation is started. However, the present invention is not limited
thereto, but at least either of them may be performed. For example,
when feeding sheets immediately after the initial swing, the
pre-job swing may be omitted, and when the feeding operation is
continuously performed, the initial swing may be omitted.
[0121] In this respect, in the present example, the detailed
description has been made of the control when the coated sheets are
used. However, the present invention is not limited thereto, but
even in any other OHP, art film, ultra-thick paper and other
standard sheets than the coated sheets which are different in
characteristic due to environment, control table may be prepared
respectively.
[0122] In the case of, for example, the OHP film or art film as
described above, since the attraction due to charging occurs under
a low-humidity environment, blowing can be performed at high wind
velocity under the low-humidity environment, and blowing can be
performed at low wind velocity under a high-humidity environment
because the attraction due to charging hardly occurs under the
high-humidity environment. Also, in the case of sheets made of
these resin materials, since moisture is not absorbed, it is not
necessary to use warm air, but therefore, the heater can be kept
OFF.
[0123] Also, in the case of the ultra-thick paper, since the
conveying resistance is increased due to its dead load and the
pickup failure occurs, there is no environmental dependence in this
case. Therefore, blowing can be performed under all environments.
Also, since no attraction due to moisture absorption occurs as in
the case of the OHP and the like, it is not necessary to use warm
air, but therefore, the heater can be kept OFF.
[0124] As described above, it may be possible to prepare a control
table for temperature for temperature control of the heater, wind
velocity, blowing time and the like which is optimum for each
material, and to provide the sheet kind input portion 21 as sheet
kind input means as shown in FIG. 4 in such a manner that the
controller 120 selects an optimum control table of time from among
a plurality of control tables of time in response to sheet kind
information from this sheet kind input portion 21 for use. Also,
since the attraction characteristic and transfer characteristic of
the coated sheet differ with kind and grade thereof, control tables
optimum for coated sheets having respective kinds and grades can be
prepared. Thereby, it is possible to provide a further highly
reliable sheet feeding apparatus.
[0125] Further, in order to re-write data of tables for time
control, control of temperature control and the like and to add new
tables, it may be also possible to provide a data input portion 22
as shown in FIG. 4 in such a manner that the user or service staffs
can freely prepare each control table already described in response
to respective uses via the data input portion 22 for storing
it.
[0126] In this respect, in the above-described example, there has
been disclosed the structure in which on the side (one end portion
of the sheets in a widthwise direction) of a sheet stack stacked on
the lifter base 16, there are arranged fans 4, 5 and air duct ports
2a, 2b to blow air on the side end of the sheet stack. However, the
present invention is not limited thereto, but can be applied to
structure in which on the front side of the sheets stacked in the
feeding direction, there is provided a air duct port so as to blow
air on the front-side end portion of the sheet stack.
[0127] In this respect, the initial swing operation and the pre-job
swing operation already described are also performed on the sheet
deck, whereby it is possible to reliably separate and feed sheets
without causing any image defects such as transfer failures.
[0128] Also, in the present example, as the sheet feeding and
separating means, there has been cited the retard system as an
example, but it goes without saying that this may be the separating
pad system or the air sheet-feeding system.
[0129] This application claims priority from Japanese Patent
Application No. 2003-301029 filed on Aug. 26, 2003, which is hereby
incorporated by reference herein.
* * * * *